Read The Manual

Talking to friends about their viva experiences is useful. Picking up on bits and pieces of what goes on in vivas while you do your PhD is inevitable.

Generally, candidates have a fair picture of what they need to do procedure-wise; the regulations might not need to be spelled out for you, but if you have any questions, concerns or “what if….” worries:

Read the manual!

Your university has one, and it will have a lot of the answers about situations and circumstances that come up around the viva.